725 



Length correction for larval and early-juvenile 

 Atlantic menhaden (Brevoortia tyrannus) 

 after preservation in alcohol 



Dariusz P. Fey 



Sea Fisheries Institute 



Dept. of Fisheries Oceanography and Marine Ecology 



ul. Kollataia 1 



81-332 Gdynia, Poland 



E-mail address dfeyg'mirgdynia pi 



Jonathan A. Hare 



NOAA National Ocean Service 



Center for Coastal Fisheries and Habitat Research 



101 Pivers Island Road 



Beaufort, North Carolina 28516-9722 



Body length measurement is an im- 

 portant part of growth, condition, 

 and mortality analyses of larval and 

 juvenile fish. If the measurements are 

 not accurate (i.e., do not reflect real 

 fish length), results of subsequent 

 analyses may be affected consider- 

 ably (McGurk, 1985; Fey, 1999; Porter 

 et al., 2001). The primary cause of 

 error in fish length measurement is 

 shrinkage related to collection and 

 preservation (Theilacker, 1980; Hay, 

 1981; Butler, 1992; Fey, 1999). The 

 magnitude of shrinkage depends on 

 many factors, namely the duration 

 and speed of the collection tow, abun- 

 dance of other planktonic organisms 

 in the sample (Theilacker, 1980; Hay, 

 1981; Jennings, 1991), the type and 

 strength of the preservative (Hay, 

 1982), and the species of fish (Jen- 

 nings, 1991; Fey, 1999). Further, fish 

 size affects shrinkage (Fowler and 

 Smith, 1983; Fey, 1999, 2001), indi- 

 cating that live length should be mod- 

 eled as a function of preserved length 

 (Pepin et al., 1998; Fey, 1999). 



The goal of this study was to ana- 

 lyze the shrinkage of late-larval and 

 early-juvenile Atlantic menhaden 

 (Brevoortia tyrannus) during pres- 

 ervation in 95% alcohol. A length 

 correction formula is presented that 

 allows live standard length to be 

 calculated from preserved standard 

 length. 



Materials and methods 



Larval and early juvenile Atlantic 

 menhaden were collected on three 

 different occasions during January- 

 March 2003 with a neuston net (2-m 2 

 opening and 947-,um mesh) deployed 

 for 2-minute durations from a bridge 

 to Pivers Island, located about 2 km 

 inside Beaufort Inlet, North Caro- 

 lina. Samples were placed in a cooler 

 and transported to the laboratory. 

 Live Atlantic menhaden larvae were 

 sorted from the samples (?i=100) and 

 their standard lengths (SL) were mea- 

 sured to the nearest 0.01 mm with a 

 caliper. All specimens (19.1-31.4 mm 

 SL) were placed in individual vials 

 filled with 95% ethyl alcohol. The fish 

 were remeasured 3. 20, and 90 days 

 after preservation. 



Repeated measures ANOVA and 

 Tukey HSD tests were used to ana- 

 lyze the significance of length changes 

 during 90 days of preservation. The 

 preserved length after 90 days was 

 than compared with live length to 

 test whether a single correction factor 

 is appropriate for a calculation of live 

 length (/-test analysis for the slope 

 difference from one). Additionally, 

 the precision of measurements was 

 evaluated by two replicate measure- 

 ments of all larvae three days after 

 preservation. Linear regression anal- 

 ysis was then used to describe the 



relationship between the two length 

 measurements. The possible deviation 

 of intercept from zero and slope from 

 one was estimated (/-test) to test for 

 the possible significant differences 

 between the two measurements. 



Results 



Time in preservative had a significant 

 effect on measured length of Atlantic 

 menhaden larvae (repeated measures 

 ANOVA, P<0.0001). Fish were sig- 

 nificantly larger prior to preservation 

 compared to three days after pres- 

 ervation (Tukey HSD, P<0.001) and 

 significantly larger three days after 

 preservation compared to 20 and 

 90 days after preservation (Fig. 1) 

 (Tukey HSD, P<0.001). When shrink- 

 age is described as a relative value, 

 the change in length that occurred 

 during the first three days of preser- 

 vation was 3.62%. Length decreased 

 by an average of 0.22% during the fol- 

 lowing 17 days and by 0.073% during 

 the remaining 70 days. 



Although smaller fish shrank pro- 

 portionally more than the larger 

 ones (/-test for H : slope = 0, P<0.001) 

 (Fig. 2A), no size effect was observed 

 when shrinkage was analyzed as 

 absolute length (regression slope = 

 0.996, SE = 0.008; H Q : slope=l; /-test 

 of regression slope, P=0.605). How- 

 ever, the ^-intercept of the regres- 

 sion of preserved length at 90 days 

 on live length was significantly 

 different from zero (regression in- 

 tercepts. 17; SE = 0.21; H : y-inter- 

 cept=0; /-test of regression intercept, 

 P<0.001) (Fig. 2B). Therefore, the 

 significantly different from zero in- 

 tercept can be used as a correction 

 factor (i.e., SL fresh = SL preserl . ed+ l.l7 

 mm). The shrinkage magnitude 

 observed by Maillet and Checkley 

 (1991) was compared to the results 

 derived in our study (Fig 2B). Their 

 formula indicated shrinkage of about 

 2% compared to approximately 4% in 

 our study. 



Manuscript submitted 31 March 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



8 February 2005 by the Scientific Editor. 



Fish. Bull. 103:725-727 (2005). 



